A reciprocating saw machine is a power saw that includes a chuck for releasably engaging the saw blade and driving the saw blade in a reciprocating motion through a work piece. The reciprocating motion can be an orbital cutting action, a straight or linear cutting action, or an angled cutting action. The length or stroke of the reciprocating motion is typically about 1½ inches or less. Reciprocating saws are sometimes referred to as recip saws, jig saws, and portable power hack saws, and the term reciprocating saw is used herein without limitation to mean reciprocating saw machines, jigsaw machines, and portable power hack machines. Reciprocating saws are typically driven by electric motors (e.g., cord or cordless saws) or are pneumatically driven. Well-known reciprocating saws are sold under the brand names “Sawzall™” by Milwaukee Electric Tool Corporation and “Tiger Saw™” by Porter-Cable Corporation.
A typical reciprocating saw blade includes a blade portion having a cutting edge defined by a plurality of teeth axially spaced relative to each other along one side of the blade, and a non-working edge formed on an opposite side of the blade relative to the cutting edge. A tang for releasably connecting the blade to the chuck of a reciprocating saw extends from an inner end of the blade. The term “recip blade” or “reciprocating saw blade” is used herein to mean a blade configured for use in a reciprocating saw.
As shown in FIG. 1, a typical prior art recip blade exhibits a tooth form defining a tip 1, a rake face 2 located on one side of the tip, and a primary clearance surface 3 located on an opposite side of the tip 1 relative to the rake face 2 defining a primary clearance angle 4, and a secondary clearance surface 5 defining a secondary clearance angle 6. As can be seen, the secondary clearance angle 6 is steeper than the primary clearance angle 4. In order to cut faster, some such prior art recip blades define relatively steep primary clearance angles, e.g., about 35° or greater. As a general matter, the steeper the clearance angle, the more sharply pointed is the tooth form, and the faster is the speed of cut but the shorter the lifespan of the tooth. One drawback associated with such prior art recip blades is that the teeth defining such steep clearance angles are relatively weak, and thus prone to premature fracture or rounding, particularly when subjected to abusive cutting applications, such as in demolition applications where cuts are made through multiple work pieces and/or multiple materials or layers of materials, such as cutting pipes or interrupted cuts of hard objects that are embedded within softer materials, like nail embedded wood, nail or screw embedded sheetrock, or plaster bonded to metal or wood lath.
Some prior art attempts to improve the performance of recip blades in such abusive cutting applications have involved increasing the thickness of the blade (i.e., the thickness of the blade body, including the thickness of the cutting teeth). For example, some recip blades define a thickness of about 0.062 inch, which is significantly thicker as compared to typical recip blades that define a thickness of about 0.05 inch. Generally, thicker blades better resist bending and twisting, which commonly occurs during abusive cutting applications. In addition, thicker teeth are more robust and are thereby suited to better handle the greater loads and stresses created during abusive cutting applications. However, although beneficial, thicker recip blades have not satisfactorily addressed the problem of premature tooth breakage and wear in abusive cutting applications.
Other prior art attempts to improve the performance of recip blades have been directed at solving the problem of premature tooth fracture and/or wear. Such prior art attempts include using different height and set styles wherein multiple teeth are set to the same height and set position to reinforce the teeth of like height and set. Although helpful, this feature has not satisfactorily addressed the problem. Another attempt to solve the problem of premature tooth fracture involves employing high-low set and/or unset teeth of varying primary and secondary clearance angles. For example, some prior art recip saw blades have recurring patterns of groups of teeth wherein each group includes a tooth with a relatively high tip, sometimes being an unset or raker tooth, and a tooth with a relatively low tip, sometimes being a set tooth, wherein the high teeth and low teeth have different primary clearance angles.
Conventional wisdom generally has taught away from such high teeth having relatively steep primary clearance angles, or even relatively shallow angles that are steeper than the primary clearance angles of the low teeth, because the relatively high teeth are the dominant teeth and the life of the blade is linked primarily to the dominant teeth. See, for example, U.S. Patent Publication No. 2008/0307936, which is incorporated by reference in its entirety as part of the present disclosure. According to conventional wisdom, if the high teeth include relatively steep primary clearance angles, or at least relatively shallow angles that are steeper than the primary clearance angles of the low teeth (e.g., about 23° or greater), the high teeth become overly exposed and subjected to excessive cutting forces during abusive cutting applications, and thus subject to fracture, chipping and/or wear. Similarly, because the low teeth are more robust, if they include relatively steeper primary clearance angles than that of the high teeth, the low teeth tend to fracture and break off the blade. However, although relatively shallow primary clearance angles of high teeth, such as angles that are shallower than that of the low teeth (e.g., less than about 23°), provide increased strength to resist tooth breakage, such high teeth tend to quickly wear and become dull during abusive cutting applications, thereby shortening the life span of the blade in such applications. As a result, the performance of prior art recip blades, such as cutting life and/or durability, has not always been at levels desired for abusive cutting applications.
Accordingly, it is an object of the present invention to overcome one or more of the above-described drawbacks and/or disadvantages of the prior art.